Electric discharge device



Oct. 4, 1955 F. OPPENHEIMER 2,719,925

ELECTRIC DISCHARGE DEVICE Filed Feb. 25, 1944 2 Sheets-Sheet 2 /OO /0/0\/0/ I03 8 s /0.9 g T T FRANK OPPENHEIMEP BY M ATTORNEY.

United States Patent ELECTRIC DISCHARGE DEVICE Frank Oppenheimer,Berkeley, Calif., assignor to the United States of America asrepresented by the United States Atomic Energy Commission ApplicationFebruary 23, 1944, Serial N0. 523,544

Claims. (Cl. 25049.5)

The present invention relates to electric discharge devices and moreparticularly to calutron ion sources.

It is an object of the invention to provide an electric discharge devicecomprising an improved arrangement for defining the cross-section of thearc discharge between the main electrodes thereof.

Another object of the invention is to provide an electric dischargedevice comprising an improved electrode arrangement for producing anelectrically stable are discharge, the ionization over any cross-sectionof which is substantially uniform.

Still another object of the invention is to provide a calutron ionsource of the arc discharge type that consumes less current for thenumber of ions produced than those ion sources heretoforeemployed.

A further object of the invention is to provide a calutron ion sourcehaving an improved electrode arrangement productive of a uniform andcopious supply of ions.

A further object of the invention is to provide a calutron ion source ofimproved construction and arrangement that is efiicient in operation andsubject to minimum wear and erosion.

A further object of the invention is to provide in an arc dischargedevice an electrode arrangement for increasing the life of the arccathode.

The invention, both as to its organization and method of operation,together with other objects and advantages thereof, will best beunderstood by reference to the following specification taken inconnection with the accompanying drawings, in which Figure 1 is adiagrammatic plan view of a calutron into which there may beincorporated an ion source embodying the present invention; Fig. 2 is adiagrammatic sectional view of the calutron taken along the line 22 inFig. 1; Fig. 3 is a schematic perspective view of the electrodearrangement in a calutron ion source embodying the present invention;Fig. 4 is a longitudinal sectional view of a calutron ion sourceembodying the present invention; Fig. 5 is a front elevation view of thecalutron ion source shown in Fig. 4; and Fig. 6 is a sectional view ofthe calutron ion source taken along the line 66 in Fig. 4.

At the outset, it is noted that a calutron is a machine of the characterof that disclosed in the copending application of Ernest 0. Lawrence,Serial No. 557,784, filed October 9, 1944, now U. S. Patent No.2,709,222, and is employed to separate the constituent isotopes of anelement and, more particularly, to increase the proportion of a selectedisotope in an element containing several isotopes in order to producethe element enriched with the selected isotope.

Such a calutron essentially comprises means for vaporizing a quantity ofmaterial containing an element that is to be enriched with a selectedone of its several isotopes; means for subjecting the vapor toionization, whereby at least a portion of the vapor is ionized causingions of the several isotopes of the element to be produced; electricalmeans for segregating the ions from the un-ionized vapor and foraccelerating the segregated ions to relatively high 2,719,925 PatentedOct. 4, 1955 ice velocities; electromagnetic means for deflecting theions along curved paths, the radii of curvature of the paths of the ionsbeing proportional to the square roots of the masses of the ions,whereby the ions are concentrated in accordance with their masses; andmeans for de-ionizing and collecting the ions of the selected isotopethus concentrated, thereby to produce a deposit of the element enrichedwith the selected isotope.

Referring now more particularly to Figs. 1 and 2 of the drawings, thereis illustrated a representative example of a calutron 10 of thecharacter noted, that comprises magnetic field structure including upperand lower pole pieces 11 and 12, provided with substantially flatparallel spaced apart pole faces, and a tank 13 disposed between thepole faces of the pole pieces 11 and 12. The pole pieces 11 and 12 carrywindings, not shown, which are adapted to be energized in order toproduce a substantially uniform and relatively strong magnetic fieldtherebetween, which magnetic field passes through the tank 13 and thevarious parts housed therein. The tank 13 is of tubular configuration,being substantially crescentshaped in plan, and comprising substantiallyflat parallel spaced-apart top and bottom walls 14 and 15, upstandingcurved inner and outer side walls 16 and 17, and end walls 18 and 19.The end walls 18 and 19 close the opposite. ends of the tubular tank 13and are adapted to be removably secured in place, whereby the tank 13 ishermetically sealed. Also, vacuum pumping apparatus, not shown, isassociated with the tank 13, whereby the interior of the tank 13 may beevacuated to a pressure of the order of 10- to 10 mm. Hg. Preferably,the component parts of the tank 13 are formed of steel, the top andbottom walls 14 and 15 thereof being spaced a short distance from thepole faces of the upper and lower pole pieces 11 and 12 respectively,the tank 13 being retained in such position in any suitable manner,whereby the top and bottom walls 14 and 15 constitute in efiect polepieces with respect to the interior of the tank 13, as explained morefully hereinafter.

The removable end wall 18 suitably supports a source unit 20 comprisinga charge receptacle 21 and a communicating arc-block 22. An electricheater 23 is arranged in heat exchange relation with the chargereceptacle 21 and is adapted to be connected to a suitable source ofheater supply, whereby the charge receptacle 21 may be appropriatelyheated, the charge receptacle 21 being formed of steel or the like. Thearc-block 22 is formed, at least partially, of carbon or graphite and issubstantially C-shaped in plan, an upstanding slot 24 being formed inthe wall thereof remote from the charge receptacle 21. Thus, thearc-block 22 is of hollow construction, the cavity therein communicatingwith the interior of the charge receptacle 21.

Also, the removable end wall 18 carries a filamentary cathode 25 adaptedto be connected to a suitable source of filament supply, the filamentarycathode 25 overhanging the upper end of the arc-block 22 and arranged inalignment with respect to the upper end of the cavity formed therein.Further, the removable end wall 18 carries an anode 26 disposed belowthe lower end of the arc-block 22 and arranged in alignment with respectto the lower end of the cavity formed therein. The anode 26 iselectrically connected to the source unit 20, which in turn is grounded;likewise the tank 13 is grounded. Also, the filamentary cathode 25 andthe cooperating anode 26 are adapted to be connected to a suitablesource of arc supply.

Further, the removable end wall 18 carries ion accelerating structure 27formed of carbon or graphite, and disposed in spaced-apart relation withrespect to the wall of the arc-block 22 in which the slot 24 is formed.More specifically, a slit 28 is formed in the ion accelerating structure27 and arranged in substantial alignment with respect to the slot 24formed in the wall of the arcblock 22. A suitable source of acceleratingelectrode supply is adapted to be connected between the arc-block 22 andthe ion accelerating structure 27, the positive and negative terminalsof the supply mentioned being respectively connected to the arc-block 22and to the ion accelerating structure 27. Further, the positive terminalof the ion accelerating potential is grounded.

The removable end wall 19 suitably supports a collector block 29 formedof stainless steel or the like and provided with two laterallyspaced-apart cavities or pockets 30 and 31 which respectivelycommunicate with aligned slots 32 and 33 formed in the wall of thecollector block 29 disposed remote from the removable end wall 19. It isnoted that the pockets 30 and 31 are adapted to receive two constituentisotopes of an element which have been separated in the calutron 10, asexplained more fully hereinafter. Further, the inner Wall 16 suitablysupports a tubular liner 34 formed of copper or the like, rectangular invertical cross-section, disposed within the tank 13 and spaced from thewalls 14, 15, 16 and 17. One end of the tubular liner 34 terminatesadjacent the accelerating structure 27; and the other end of the tubularliner 34 terminates adjacent the collector block 29; the tubular liner34 constituting an electrostatic shield for the high velocity ionstraversing the curved paths between the slit 28 formed in the ionaccelerating structure 27 and the slots 32 and 33 formed in thecollector block 29, as explained more fully hereinafter. Finally, thetubular liner 34 is electrically connected to the ion acceleratingstructure 27 and to the collector block 29. Thus, it will be understoodthat the source unit and the tank 13 are connected to the positivegrounded terminal of the accelerating electrode supply; while the ionaccelerating structure 27, the tubular liner 34 and the collector block29 are connected to the ungrounded negative terminal of the acceleratingelectrode supply; the ion accelerating structure 27, the tubular liner34 and the collector block 29 being electrically insulated from thecomponent parts of the tank 13.

Considering now the general principle of operation of the calutron 10, acharge comprising a compound of the element to be treated is placed inthe charge receptacle 21, the compound of the element mentioned beingone which may be readily vaporized. The end walls 18 and 19 are securelyattached to the open ends of the tank 13, whereby the tank 13 ishermetically sealed. The various electrical connections are completedand operation of the vacuum pumping apparatus, not shown, associatedwith the tank 13 is initiated. When a pressure of the order of 10 to 10mm. Hg is established within the tank 13, the electric circuits for thewindings, not shown, associated with the pole pieces 11 and 12 areclosed and adjusted, whereby a predetermined magnetic field isestablished therebetween traversing the tank 13. The electric circuitfor the heater 23 is closed, whereby the charge in the charge receptacle21 is heated and vaporized. The vapor fills the charge receptacle 21 andis conducted into the communicating cavity formed in the arc-block 22.The electric circuit for the filamentary cathode 25 is closed, wherebythe filamentary cathode is heated and rendered electron emissive. Thenthe electric circuit between the filamentary cathode 25 and the anode 26is closed, whereby an arc discharge is struck therebetween, electronsproceeding from the filamentary cathode 25 to the anode 26. Theelectrons proceeding from the filamentary cathode 25 break up themolecular form of the compound of the vapor to a considerable extent,producing positive ions of the element that is to be enriched with theselected one of its isotopes.

The electric circuit between the arc-block 22 and the ion acceleratingstructure 27 is completed, the ion accelerating structure 27 being at ahigh negative potential with respect to the arc-block 22, whereby thepositive ions in the arc-block 22 are attracted by the ion acceleratingstructure 27 and accelerated through the voltage impressed therebetween.More particularly, the positive ions proceed from the cavity formed inthe arc-block 22 through the slot 24 formed in the Wall thereof, andacross the space between the ion accelerating structure 27 and theadjacent wall of the arc-block 22, and thence through the slit 23 formedin the ion accelerating structure 27 into the interior of the tubularliner 34. The high-velocity positive ions form a vertical upstandingribbon or beam proceeding from the cavity formed in the arc-block 22through the slot 24 and the aligned slit 28 into the tubular liner 34.

As previously noted, the collector block 29, as well as the tubularliner 34, is electrically connected to the ion accelerating structure27, whereby there is an electricfield-free path for the high-velocitypositive ions disposed between the ion accelerating structure 27 and thecollector block 29 within the tubular liner 34. The high-velocitypositive ions entering the adjacent end of the liner 34 are deflectedfrom their normal straight-line path and from a vertical plane passingthrough the slot 24 and the aligned slit 28, due to the effect of therelatively strong magnetic field maintained through the space within thetank 13 and the liner 34 through which the positive ions travel, wherebythe positive ions describe arcs, the radii of which are proportional tothe square roots of the masses of the ions and consequently of theisotopes of the element mentioned. Thus, ions of a relatively lightisotope of the element describe an interior arc of relatively shortradius and are focused through the slot 32 into the pocket 30 formed inthe collector block 29; whereas ions of a relatively heavy isotope ofthe element describe an exterior arc of relatively long radius and arefocused through the slot 33 into the pocket 31 formed in the collectorblock 29. Accordingly, the relatively light ions are collected in thepocket 30 and are de-ionized to produce a deposit of the relativelylight isotope of the element therein; while the relatively heavy ionsare collected in the pocket 31 and are de-ionized to produce a depositof the relatively heavy isotope of the element therein.

After all of the charge in the charge receptacle 21 has been vaporized,all of the electric circuits are interrupted and the end wall 18 isremoved so that another charge may be placed in the charge receptacle 21and subsequently vaporized in the manner explained above. After asuitable number of charges has been vaporized in order to obtainappropriate deposits of the isotopes of the element in the pockets 3tand 31 of the collector block 29, the end Wall 19 may be removed and thedeposits of the collected isotopes in the pockets 30 and 31 in thecollector block 29 may be reclaimed.

Of course, it will be understood that the various dimensions of theparts of the calutron 10, the various electrical potentials appliedbetween the various electrical parts thereof, as well as the strength ofthe magnetic field between the pole pieces 11 and 12, are suitablycorrelated with respect to each other, depending upon the mass numbersof the several isotopes of the element that is to be treated therein.

In the operation of the calutron 10, it is highly desirable that arelatively intense stable beam of positive ions be projected by the ionaccelerating structure 27, through the liner 34, toward the collectorblock 29; which operating condition requires that the source unit 20 beproductive of a steady and copious supply of positive ions. Toaccomplish this end in the source unit 20, the arc discharge through thecavity in the arc-block 22 between the filamentary cathodc 25 and theanode 26 must be both relatively intense and uniform. Moreover, it isdesirable that such an arc discharge should be steady and free from bothintensity and position variations in order that the ion source unit 20be productive of a highly Continuous, copious and uniform supply ofpositive ions. Furthermore, the ion source unit 20 should be soconstructed and arranged that the parts thereof are subjected to minimumwear and erosion, whereby the unit has a long life and an efficientoperating characteristic.

While the source unit in the calutron disclosed in the previouslymentioned copending application of Ernest 0. Lawrence is satisfactory inoperation, it does not possess the characteristics noted to the extentdesired; nor has it the long life required for most efiicient commercialoperation.

Referring now more particularly to Fig. 3 of the drawing, the electrodearrangement in a calutron ion source 100 embodying the features of thepresent invention is illustrated schematically in perspective. Moreparticularly, this calutron ion source 100 comprises, among otherelements, a substantialy U-shaped filamentary cathode 121 formed oftungsten, tantalum, or the like, a plate-like anode 127 formed oftungsten or the like, and a plate-like collimating electrode 124 formedof tungsten, molybdenum or the like. The electrodes mentioned arearranged in the magnetic field of the calutron, the direction of thefield between the north pole and the south pole of the field structurebeing indicated by the arrow 53. The filamentary cathode 121 and theanode 127 are arranged in substantially parallel longitudinalspacedapart relation and are aligned with the magnetic field mentioned;While the collimating electrode 124 is arranged between the filamentarycathode 121 and the anode 127 in substantially parallel relationtherewith and in alignment with the magnetic field mentioned. Thecollimating electrode 124 has an elongated, transversely extending slot125 formed therethrough and disposed in alignment with the centralportion of the U- shaped filamentary cathode 121, the collimatingelectrode 124 being disposed closely adjacent the filamentary cathode121. Accordingly, the filamentary cathode 121, the collimating electrode124 and the anode 127 are respectively disposed in three substantiallyparallel planes spaced apart longitudinally and disposed substantiallynormal to the magnetic field mentioned. Furthermore, the central portionof the filamentary cathode 121, the slot 125 formed in the collimatingelectrode 124 and the central portion of the anode 127 are arranged inalignment with the magnetic field mentioned.

Considering now the structural and dimensional details of the electrodesmentioned, it is noted that the slot 125 formed in the collimatingelectrode 124 is narrower than the corresponding width of the centralportion of the filamentary cathode 121 and is shorter in the transversedirection than the length of the central portion of the filamentarycathode 121, whereby the dimensions of the slot 125 formed in thecollimating electrode 124 are less than the corresponding dimensions ofthe filamentary cathode 121 disposed thereabove. In the embodiment ofthe calutron ion source 100 illustrated, highly satisfactory resultshave been obtained employing a flat filamentary cathode 121 formed oftungsten, the central portion of the filamentary cathode beingsubstantially 0.060" thick, 0.150 wide and 1.000" long; an anode 127formed of tungsten, 0.125" thick, 0.687" wide and 1.063 long; and acollimating electrode 124 formed of tungsten, 0.100" thick, 0.625 wideand 1.250 long, the centrally disposed slot 125 formed therein being0.094 wide and 0.625" long. Also, in this embodiment the collimatingelectrode 124 was disposed approximately 0.125 below the filamentarycathode 121; and the filamentary cathode 121 and the anode 127 werespaced apart about 12".

The filamentary cathode 121 is electrically connected by way of anadjustable resistor 54 to a source of filament supply indicated as abattery 55; while the filamentary cathode 121 and the anode 127 arerespectively connected to the negative and positive terminals of asuitable source of arc supply. The collimating electrode 124 iselectrically connected to the anode 127, whereby a substantiallyelectric-field-free zone is defined therebetween in the gaseous regionin the arc-block.

Considering now the general principle of operation of the sourceunit100, the filamentary cathode 121 is heated and rendered electronemissive and the arc supply circuit is completed, rendering thefilamentary cathode 121 negative with respect to the collimatingelectrode 124 and the anode 127. Accordingly, electrons are projectedfrom the filamentary cathode 121 toward the collimating electrode 124along the magnetic field 53. Some of these electrons pass through theslot 125 formed in the collimating electrode 124 and continue toward theanode 127, whereby the gas or vapor in the zone disposed between thecollimating electrode 124 and the anode 127 in the gaseous or vaporregion is ionized. More specifically, the electrons projected from thefilamentary cathode 121 gain substantially all of their energy intraversing the electric field between the filamentary cathode 121 andthe collimating electrode 124, whereby they enter the gaseous or vaporregion at velocities higher than that required for ionization. Moreover,the elec trons traveling between the filamentary cathode 121 and theanode 127 are, for the most part, confined to paths along the magneticfield, inasmuch as any horizontal motion imparted to these electronswill result in their traveling along helices of extremely small radii,the axes of the helices being along the magnetic field.

In view of the fact that the dimensions of of the slot 125 formed in thecollimating electrode 124 are less than the corresponding dimensions ofthe filamentary cathode 121 disposed thereabove, the cross-section ofthe electron stream entering the gaseous region disposed between thecollimating electrode 124 and the anode 127 is positively defined andelectrons only from the uniform electron emissive surface of the centralportion of the filamentary cathode 121 are employed. This uniform andsteady stream of electrons in the gas or vapor region mentioned resultsin a discharge therethrough, whereby a uniform copious supply ofpositive ions is produced. This discharge through this region is of thearc type, being characterized by a high current, a low voltage drop anda luminous plasma. More specifically, most of the electrons projectedfrom the filamentary cathode 121 through the slot 125 in the collimatingelectrode 124 proceed to the anode 127, thereby to complete the circuitbetween the positive and negative terminals of the arc supply, currentin the arc discharge flowing from the anode 127 to the filamentarycathode 121. Some of the positive ions produced in the region disposedbetween the collimating electrode 124 and the anode 127 travel throughthe slot 125 in the collimating electrode 124 and bombard thefilamentary cathode 121; while the useful positive ions produced in theregion mentioned are drawn oif by the ion accelerating structure andprojected into the associated liner and ultimately collected in thecollector block in the calutron in the manner previously described. Itshould be noted that the zone disposed between the collimating electrode124 and the anode 127 is believed to be substantiallyelectric-field-free, the electric field in this zone, bothlongitudinally and transversely, being of the order of only a few volts.

Due to the construction and arrangement of the electrodes of the ionsource, the stream of electrons proceeding from the filamentary cathode121 through the slot 125 formed in the collimating electrode 124 to theanode 127 is of ribbon-like configuration, within the boundary of whichsubstantially all of the positive ions are formed in the gas or vaporregion. This arrangement positively insures a uniform copious supply ofpositive ions presenting a well-defined surface to the slit in the wallof the arcblock with which the ion accelerating structure is operativelyassociated. Another advantage of this arrangement is the protectionaiforded the filamentary cathode 121 from excessive positive ionbombardment. Inasmuch as the positive ions which travel toward thefilamentary cathode 121 are limited by the arc collimating slot 125formed in the collimating electrode 124, the resulting alloying andpitting of the filamentary cathode 121 is thus substantially reduced,and consequently the life of the filamentary cathode 121 is increased.Further, the collimating electrode 124 aids in confining the vapor to beionized to the region between the collimating electrode 124 and theanode 127, restricting the passage of the vapor into the neighborhood ofthe filamentary cathode 121, thus reducing the accumulation of condensedvapor and deposited material around the filamentary cathode 121.

Referring now more particularly to Figs. 4 to 6, inclusive, of thedrawings, there are illustrated the structural details of the calutronion source unit which is arranged in the magnetic field between the polepieces of the calutron in the manner previously explained, the ionsource unit 100 comprising a charge receptacle 101 and an arc-block 102.The charge receptacle 101 comprises wall structure, including aremovable cover 101a, defining an upstanding cylindrical cavity 103therein, that is adapted to receive a removable cylindrical chargebottle 104 containing a charge 105 which is to be vaporized. Thearc-block 102 comprises wall structure defining an upstanding diffusionchamber 106 and an upstanding arc chamber 107 therein, the cavity 103communicating with the diffusion chamber 106 through a tubular member108 supported by the wall structure of the charge receptacle 101 and thewall structure of the arc-block 102. The wall structure of the chargereceptacle 101 carries an exteriorly arranged electric heater 109 of anysuitable form, whereby the charge receptacle 101 and consequently thecharge bottle 104 may be appropriately heated in order to vaporize thecharge 105 contained in the charge bottle 104. Similarly, the wallstructure of the arc-block 102 carries an exteriorly arranged electricheater 110 of any suitable form, whereby the arc-block 102, and moreparticularly the diffusion chamber 106 therein, may be heated in orderto prevent condensation of the contained vapor, as explained more fullyhereinafter.

More particularly, the wall structure of the arc-block 102 comprises asubstantially inverted U-shaped frame member 111, supporting anupstanding bafile plate 112, the frame member 111 and the bafiie plate112 being formed of carbon or graphite. The frame member 111 is securedto the wall structure of the arc-block 102 by an arrangement comprisingtwo upstanding strips 113, and comprises a top wall 114, two upstandingsubstantially parallel spaced-apart side walls 115 and a front wall 116,the front wall 116 having a centrally disposed longitudinal slot 117formed therein and communicating with the arc chamber 107. The sideedges of the battle plate 112 are spaced a short distance from the sidewalls 115 of the frame member 111 in order to provide communicationbetween the diffusion chamber 106 and the arc chamber 107, the baffieplate 112 defining the boundary between the chambers mentioned.

The wall structure of the charge receptacle 101 carries a standard 113which supports cathode structure 119 in cooperating relationship withrespect to the arc-block 102. More particularly, the cathode structure119 comprises two terminals 120 supporting the opposite ends of thesubstantially U-shaped filamentary cathode 121, the opposite ends of thefilamentary cathode 121 being removably clamped in place by therespective terminals 120, and the two terminals being connected to thesuitable source of filament supply, as previously noted. The centralportion of the filamentary cathode 121 overhangs the central portion ofthe top wall 114 of the frame member 1111, the top wall 114 having atransversely extendh ing slot 122 formed therethrough communicating Withthe arc chamber 107. The upper end of the transverse slot 122 isprovided with a counter-recess 123 extending thereabout which receivesthe collimating electrode 124, the collimating electrode 124 having thetransversely extending slot 125 formed therethrough, as previouslynoted, and communicating with the transverse slot 122 formed in the topwall 114 and consequently with the arc chamber 107, the length of theslot 125 being greater than the width of the slot 117 formed in thefront wall 116. More particularly, the filamentary cathode 121 is spaceda short distance above the collimating electrode 124, the centralportion of the filamentary cathode 121 being arranged in alignment withthe tranverse slot 125 formed in the collimating electrode 124. Further,a laterally extending slot 126 is formed in the front wall 116 of theframe member 111 adjacent the lower end thereof, and supports the anode127 extending into the arc chamber 107 in alignment with the centralportion of the filamentary cathode 121 and the transverse slot 125formed in the collimating electrode 124.

The negative and positive terminals of the arc supply are respectivelyconnected to the filamentary cathode 121 and to the arc-block 102, theanode 127 and the collimating electrode 124 being connected together bythe frame member 111, and consequently by way of the arcbloclc 102 tothe positive terminal of the arc supply mentioned, as previously noted.Finally, a shield 128 is supported by one of the terminals 120 andextends laterally over the upper surface of the central portion of thefilamentary cathode 121 in order to prevent migration of the electronsemitted by the filamentary cathode 121 upwardly in the longitudinaldirection.

Considering now the detailed operation of the calutron ion source 100,when the electric circuit for the heater 109 is completed, the chargereceptacle 101 and consequently the charge bottle 104 are heated,whereby the charge 105 is vaporized, filling the cavity 103 in thecharge receptacle 101. The vapor passes through the tubular member 108into the diffusion chamber 106, whereby this chamber is filled with thevapor. The vapor is thoroughly dilfused in the diffusion chamber 106 andpasses around the side edges of the baffle plate 112 into the arcchamber 107, whereby this chamber is filled with the vapor. Moreparticularly, the arc chamber 107 is thoroughly and uniformly filledwith the vapor to be ionized, due to the arrangement of the diffusionchamber 106 and the baffie plate 112.

When the circuit for the filamentary cathode 121 is completed, thefilamentary cathode 121 is heated and rendered electron emissive; andwhen the arc supply circuit is completed between the filamentary cathode121 and the arc-block 102, electrons are projected from the centralportion of the filamentary cathode 121 toward the collimating electrode124. More particularly, some of these electrons pass through thetransverse slot 125 formed in the collimating electrode 124 into the arcchamber 107 and proceed toward the anode 127. Accordingly, thecollimating electrode 124 causes a stream of electrons having aribbon-like configuration to be projected through the arc chamber 107,whereby the vapor in the arc chamber 107 is ionized. Moreover, the widthof the stream of electrons is greater than the width of the upstandingslot 117 formed in the front wall 116, whereby any vapor flowing throughthe arc chamber 107 and the slot 117 must traverse the electron streamand thus be subjected to its ionizing influence. The positive ionsproduced in the arc chamber 107 are drawn through the upstanding slot117 formed in the front wall 116 of the frame member 111 by theassociated ion accelerating structure, whereby a beam of positive ionshaving a substantially ribbon-like configuration is projected into theadjacent end of the associated liner and directed toward the cooperatingcollector block.

While there has been described what is at present considered to be thepreferred embodiment of the invention, it will be understood thatvarious modifications may be made therein and it is intended to cover inthe appended claims all such modifications as fall within the truespirit and scope of the invention.

What is claimed is:

1. An ion source comprising means for establishing a magnetic field, ahollow arc-block positioned therein defining an arc region, an electronemitter positioned adjacent to said are region and aligned in themagnetic field with respect thereto, an anode disposed within saidarcblock and connected electrically thereto, and an apertured electrodepositioned between said electron emitter and said are region and madeelectrically positive relative to the electron emitter, said electrodebeing connected electrically to said anode, the opening of saidelectrode being less than the emitting portion of said electron emitteras projected along said magnetic field, whereby a selected part only ofthe electron emission may be projected into the are region.

2. An ion source comprising means for establishing a magnetic field, ahollow arc block positioned therein and having an exit openingtransverse to said magnetic field, two electrical terminals positionedadjacent to said are block, a filament connected to said terminals andhaving an intermediate section adapted to be thermally emissive, meansfor supplying electric current to said terminals, an anode disposedwithin said arc-block and connected electrically thereto, means formaking the arc block electrically positive with respect to the filament,an aperture in said are block aligned with said filament in saidmagnetic field and having an opening less than the emitting section ofsaid filament aligned therewith, whereby the most intense and steadyelectron emission is selected for entry into said hollow arc block andmovement to said anode, and means for supplying gas to said are blockwhereby said gas is ionized by said electron emission.

3. An ion source comprising means for establishing a magnetic field, ahollow arc block positioned therein having an apertured wall alignedwith the magnetic field and an end wall substantially transversethereto, an anode disposed within said arc-block and connectedelectrically thereto, said end wall having an opening therein thatparallels the inner edge of the magnetically aligned wall and thatextends along said aligned wall for a greater distance than the edges ofthe aperture therein, an electrically negative electron emitter placedover said opening and having an emission surface as projected along themagnetic field greater than the opening area, and means for supplyinggas to said hollow arc block, the gas passing through the electronstream before exiting through said aperture.

4. An ion source comprising in combination, an enclosed chambercontaining an ionizable vapor, an exit slot in said chamber confiningthe vapor in its passage therefrom, an anode within said chamberadjacent one extremity of said slot, an elongated cathode having itslonger dimension arranged transversely of said slot adjacent the otherextremity thereof on the side nearer the chamber, an electrode plateinterposed between the anode and cathode and provided with an aperturesmaller in length and width than said cathode, said plate beingconnected electrically to said anode, said aperture being longer thanthe width of the slot and occupying a similar relative position as thecathode with respect to said slot, means for producing an arc dischargebetween said cathode and anode and through the aperture in saidelectrode plate, whereby the resulting ribbonlike configuration ofdischarge provides a curtain through which substantially all of thevapor passes on its way through said exit slot.

5. An ion source comprising, means for establishing a magnetic field, ahollow arc-block therein enclosing a gaseous region, a cathode disposedadjacent one end of said arc-block and having an electron emittingsurface, an anode disposed adjacent the other end of said arc-block andaligned with said cathode with respect to said field, means forproducing an arc discharge between said cathode and said anode throughsaid region, whereby the gas in said region is ionized, a memberdisposed between said cathode and said anode adjacent said cathode andhaving an elongated slot magnetically aligned with a part only of saidelectron emitting surface and defining the cross section of said aredischarge through said region, said member and said anode beingconnected electrically, whereby said are discharge between said cathodeand said anode through said region has a configuration corresponding tosaid slot, means for admitting gas to be ionized through an opening insaid arc-block into said region, said arc-block having a slit extendingalong said magnetic field in a wall thereof communicating with saidregion, and means for drawing a beam of ions from said region throughsaid slit.

References Cited in the file of this patent UNITED STATES PATENTS OTHERREFERENCES Tuve et al.: Physical Review, August 1, 1935, vol. 48, pp.241-256.

Bleakney: Physical Review, May 15, 1932, vol. 40,

